In Kaiserreich, there is an event if Austria conquers Germany, they can either release it as a puppet, do. nothing(But lose 300 PP) or for the German empire (and lose only 100 PP, but gain cores on everything)

Mine appears to be bugged however as I did not core Germany. Also the event kept firing even after I became the German Empire, I eventually chose "Occupy everything" for 300 PP to get the events to stop firing.